Bsurface error problem
I have had similar issues with Bsurfaces and it is difficult to pin point what triggers the error. The solution that works for me is making sure the automatic join is not ticked. 



For the record: The error, when it happens, generates a number of overlapping files which essentially corrupt further work - specifically 4 files. In my case here only the Plane [green] can be considered not corrupt and the only one worth saving. I would advise that the other items be deleted, your file saved and Blender restarted.